How much money would you get if you put two pound fifty on a 9 to 1 odd?

So long as you put the £2.50 on "to win", and this 9/1 bet did actually win, the total amount you would get back is £25.00.

This is calculated at (9 x £2.50) / 1 = £22.50, plus your original stake back of £2.50.